Main rotor blade with integral tip section

ABSTRACT

A main rotor blade assembly includes a tip spar which defines a tip spar non-straight form, an upper blade skin which defines an upper blade skin non-straight form adjacent to the tip spar non-straight form and a lower blade skin which defines a lower blade skin non-straight form adjacent to the tip spar non-straight form.

The present invention is a continuation of U.S. patent application Ser.No. 11/953,440, filed Dec. 10, 2007.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support with the United StatesNavy under Contract No.: N00019-06-C-0081. The government therefore hascertain rights in this invention.

BACKGROUND OF THE INVENTION

The present invention relates to a rotary wing aircraft main rotorblade, and more particularly to a main rotor blade tip arrangement.

Rotary-wing aircraft rotor blades often include an anhedral tip sectionof a selected sweep, taper, and form to increase blade performance.Anhedral tip sections increase hover performance and lift capabilitiesof a rotary wing aircraft. Rotor blade tip sections are subjected tosignificant stresses/strains due to aerodynamic forces, andconcomitantly experience significant structural degradation due to wearand abrasion. These aerodynamic forces may be increased upon a tipsection with an anhedral form due to the loads induced thereby.

Conventional anhedral tip sections require numerous components to carrythe loads induced by the anhedral form. Conventional anhedral tipsections may include two structural anhedral tip skins, two structuralcores along with various non-structural components and redundantfasteners.

SUMMARY OF THE INVENTION

A main rotor blade assembly according to an exemplary aspect of thepresent invention includes: a main spar; a main core adjacent to themain spar; a tip spar attached to the main spar in an overlaprelationship, the tip spar defining a tip spar non-straight form; anupper blade skin adjacent to the main spar and the tip spar, the upperblade skin defining an upper blade skin non-straight form adjacent tothe tip spar non-straight form; and a lower blade skin adjacent to themain spar and the tip spar the upper blade skin defining a lower bladeskin non-straight form adjacent to the tip spar non-straight form.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently disclosed embodiment. The drawings thataccompany the detailed description can be briefly described as follows:

FIG. 1 is a perspective view of a rotary wing aircraft for use with thepresent invention;

FIG. 2A is a perspective view of a main rotor blade;

FIG. 2B is an expanded perspective view of a tip section of the rotorblade of FIG. 2A;

FIG. 3 is an exploded view of a main rotor blade;

FIG. 4 is an exploded view of a removable tip cap for a main rotorblade;

FIG. 5A is a plan view of a tip section of a main rotor blade;

FIG. 5B is a top plan view of a main rotor blade;

FIG. 5C is an exploded view of a tip section of the main rotor blade;

FIG. 5D is an expanded view of a distal end of a tip spar assemblywithout a tip cap mounted thereto;

FIG. 5E is an expanded section view of a tip spar bonded to a main bladespar with a tip cap installed to the tip spar; and

FIG. 6 is a chart illustrating one manufacturing plan of a main rotorblade in accordance with one non-limiting embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENT

FIG. 1 schematically illustrates a rotary-wing aircraft 10 having a mainrotor system 12. The aircraft 10 includes an airframe 14 having anextending tail 16 which mounts a tail rotor system 18, such as ananti-torque system. The main rotor assembly 12 is driven about an axisof rotation A through a main gearbox (illustrated schematically at T) byone or more engines E. The main rotor system 12 includes a multiple ofrotor blade assemblies 20 mounted to a rotor hub H. Although aparticular helicopter configuration is illustrated and described in thedisclosed non-limiting embodiment, other configurations and/or machines,such as high speed compound rotary wing aircraft with supplementaltranslational thrust systems, dual contra-rotating, coaxial rotor systemaircraft, turbo-props, tilt-rotors and tilt-wing aircraft, will alsobenefit from the present invention.

Referring to FIG. 2A, each rotor blade assembly 20 of the rotor assembly12 generally includes a root section 22, an intermediate section 24, atip section 26 and a tip cap 28. Each rotor blade section 22, 24, 26, 28may define particular airfoil geometries to particularly tailor therotor blade aerodynamics to the velocity increase along the rotor bladespan. The rotor blade tip section 26 includes an anhedral form 27 (FIG.2B), however, any angled and non-angled forms such as cathedral, gull,bent, and other non-straight forms will benefit from the presentinvention. The anhedral form 27 as defined herein may include a rotorblade tip section 26 which is at least partially not contained in aplane defined by the intermediate section 24.

The rotor blade sections 22-28 define a span R of the main rotor bladeassembly 20 between the axis of rotation A and a distal end 30 of thetip cap 28 such that any radial station may be expressed as a percentagein terms of a blade radius x/R. The rotor blade assembly 20 defines alongitudinal feathering axis P between a leading edge 32 and a trailingedge 34. The distance between the leading edge 32 and the trailing edge34 defines a main element chord length Cm.

Referring to FIG. 3, the rotor blade assembly 20 generally includes amain blade assembly 40 and a tip assembly 42. The main blade assembly 40includes an upper skin 44 a main core 46, a main spar 48, a lower skin50, and a leading edge assembly 52. The main spar 48, main core 46 andskins 44, 50 are generally referred to as a pocket assembly, the forwardportion of which is closed out by the leading edge assembly 52.

The leading edge assembly 52 generally includes a main sheath laminate54 upon which is mounted a wear-resistant material such as a titaniumerosion strip 56 and a nickel erosion strip 58 to provide abrasionprotection. Alternatively, the sheath laminate 54 may include a singleerosion strip 60 manufactured of AM355 which replaces the titaniumerosion strip 56 and the nickel erosion strip 58. It should beunderstood that a variety of a wear-resistant materials mayalternatively or additionally be provided for the leading edge assembly52. Additional structures such as weight cups 62, blade tie downfastener structures 64 and trim tab systems 66 may also be provided,further details of which need not be further elaborated herein.

The tip assembly 42 generally includes a tip spar 48T, a tip core 46T, atip leading edge assembly 68 and the tip cap 28. The tip cap 28 may beremovably attached to the tip spar 48T though hardware 70 in a capinterface 78 (FIG. 4) to close-out the end of the tip assembly 42. Thecap interface 78 may be defined at an inboard radial station 77 ofapproximately ninety eight percent (98% x/R) and end at an outboardradial station 79 which defines the distal end of the tip spar 48T,however other locations may alternatively be provided. It should beunderstood that other overlap lengths, locations and interfaces mayalternatively or additionally be provided.

The tip leading edge assembly 68 may also include a splice cap laminate54T and a tip erosion strip 72 to provide abrasion protection. Thesplice cap laminate 54T abuts the main sheath laminate 54 at a tipinterface 84 while the tip erosion strip 72 may overlap the tipinterface 84 therebetween. The tip cap 28 also includes an erosion cap76 which may overlap the tip cap interface 78 between the tip assembly42 and the tip cap 28. The tip erosion strip 72 and the erosion cap 76may include AM355, titanium, nickel, or a variety of otherwear-resistant materials or combinations thereof.

Referring to FIG. 5A, the main spar 48 and the tip spar 48T extend alongthe length of the sections 22-26. The main spar 48 and the tip spar 48Tare structural members manufactured of a high strength non-metalliccomposite material and/or high strength metallic material such astitanium. The main spar 48 is attached to the tip spar 48T in amale-female overlap relationship 80. The upper skin 44 and the lowerskin 50 extend outboard of the overlap relationship 80 which allows acontiguous composite skin laminate from the root section 22 through thetip section 26 to define the aerodynamic shape of the blade (FIG. 5B).That is, no separate main skins and tip skins are utilized. In onenon-limiting embodiment, the upper skin 44 and the lower skin 50 extendfrom the root section 22 to the inboard radial station 77 of the capinterface 78 of the tip spar 48T which abuts the tip cap 28. In otherwords, the upper skin 44 and the lower skin 50 extend past the overlaprelationship 80. Lift properties, for example, are significantlyincreased over conventional rotor blades with separate tip skins due inpart to the increased strength of the one-piece composite skin laminate.Should a blade strike occur, the tip assembly 42 will still separatefrom the main blade assembly 40 at the tip interface 82 such that onlythe tip spar 48T and related tip assembly 42 components may break awaywhich thereby allows the main blade 20 defined by the main spar 48 toremain flightworthy, albeit with reduced lift capabilities.

The tip spar 48T and the tip core 46T define the anhedral form or otherangled and non-angled forms such as cathedral, gull, bent, and others.Furthermore, the tip core 46T may be hot formed to specifically includethe anhedral form as well as be of similar or different weight per cubicfoot (pcf) as compared to the main core 46 to provide particular liftand strength properties. The anhedral form may be located at a radialstation of approximately ninety six percent (96% x/R). It should beunderstood that the anhedral form or other angled and non-angled formsmay be located at other radial stations.

An end section ST of the tip spar 48T is bonded over an end section SMof the main spar 48 (FIG. 5C) to define the overlap relationship 80. Anadhesive material, such as epoxy film adhesive, is one example of abonding agent. The main spar end section SM may be of a reducedperimeter such that a flush outer mold line (OML) spar surface is formedtherebetween. That is, the end section SM of the main spar 48 defines ajogged or stepped area to receive the end section ST of the tip spar48T. The overlap relationship 80 may begin at an inboard radial station82 of approximately eighty nine percent (89% x/R) and end at an outboardradial station 84 of approximately ninety two percent (92% x/R). Itshould be understood that other overlap length, locations and interfacesmay alternatively or additionally be provided.

Referring to FIG. 5C, the tip spar 48T may include a forward tip sparsection 48Tf and an aft tip spar section 48Ta. The forward tip sparsection 48Tf includes an open aft section 90 with a stepped inner moldline to receive the open aft section 90 of the forward tip spar section48Tf of FIG. 5D. The aft tip spar section 48Ta includes an open forwardsection 92 with a stepped outer mold line. It should be understood thatother overlap length, locations and interfaces may alternatively oradditionally be provided. The forward and aft split arrangementfacilitates assembly of the forward tip spar section 48Tf to the aft tipspar section 48Ta and the end section ST of the tip spar 48T over theend section SM of the main spar 48 (FIG. 5E). Assembly and manufactureof the main rotor blade assembly 20 may generally follow themanufacturing plan as schematically illustrated in FIG. 6.

It should be understood that relative positional terms such as“forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like arewith reference to the normal operational attitude of the vehicle andshould not be considered otherwise limiting.

It should be understood that although a particular component arrangementis disclosed in the illustrated embodiment, other arrangements willbenefit from the instant invention.

Although particular step sequences are shown, described, and claimed, itshould be understood that steps may be performed in any order, separatedor combined unless otherwise indicated and will still benefit from thepresent invention.

The foregoing description is exemplary rather than defined by thelimitations within. Many modifications and variations of the presentinvention are possible in light of the above teachings. The disclosedembodiments of this invention have been disclosed, however, one ofordinary skill in the art would recognize that certain modificationswould come within the scope of this invention. It is, therefore, to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described. For thatreason the following claims should be studied to determine the truescope and content of this invention.

1. A main rotor blade assembly comprising: a main spar; a main coreadjacent to said main spar; a tip spar attached to said main spar in anoverlap relationship, said tip spar defining a tip spar non-straightform; an upper blade skin adjacent to said main spar and said tip spar,said upper blade skin defining an upper blade skin non-straight formadjacent to said tip spar non-straight form; and a lower blade skinadjacent to said main spar and said tip spar said upper blade skindefining a lower blade skin non-straight form adjacent to said tip sparnon-straight form.
 2. The main rotor blade assembly as recited in claim1, wherein said tip spar is attached to said main spar in an overlaprelationship.
 3. The main rotor blade assembly as recited in claim 2,wherein said overlap relationship comprises an end section of said mainspar.
 4. The main rotor blade assembly as recited in claim 3, whereinsaid end section of said main spar comprises a reduced perimeter steppedsection to receive said tip spar.
 5. The main rotor blade assembly asrecited in claim 2, wherein said overlap relationship extends between aninboard radial station of approximately eighty nine percent (89% x/R)and an outboard radial station of approximately ninety two percent (92%x/R).
 6. The main rotor blade assembly as recited in claim 1, whereinsaid blade skin is contiguous over an interface of said overlaprelationship.
 7. The main rotor blade assembly as recited in claim 6,wherein said tip spar non-straight form defines an anhedral form.
 8. Themain rotor blade assembly as recited in claim 7, wherein said tip sparnon-straight form defines a swept form.
 9. The main rotor blade assemblyas recited in claim 8, wherein said anhedral form is defined at anapproximately ninety six percent a radial station (96% x/R).
 10. Themain rotor blade assembly as recited in claim 8, wherein said upperblade skin non-straight form and said lower blade skin non-straight formis defined at an approximately ninety six percent a radial station (96%x/R).
 11. The main rotor blade assembly as recited in claim 1, whereinsaid main core abuts said main spar along a main core forward surfaceand said tip core abuts said tip spar along a tip core forward surface.12. The main rotor blade assembly as recited in claim 11, wherein saidtip core defines an anhedral form at an approximately ninety six percenta radial station (96% x/R).
 13. The main rotor blade assembly as recitedin claim 1, wherein said tip spar comprises a forward tip spar sectionand an aft tip spar section.
 14. The main rotor blade assembly asrecited in claim 13, wherein said forward tip spar section comprises anopen aft section with a stepped inner mold line.
 15. The main rotorblade assembly as recited in claim 13, wherein said aft tip spar sectioncomprises an open forward section with a stepped outer mold line. 16.The main rotor blade assembly as recited in claim 13, wherein saidforward tip spar section comprises an open aft section with a steppedinner mold line to receive said aft tip spar section which comprises anopen forward section with a stepped outer mold line.
 17. The main rotorblade assembly as recited in claim 1, further comprising a tip capremovably mounted to said tip spar at a tip cap interface.